1. Field of the Invention
The present invention relates to a sheet for mounting a workpiece to be polished (herein referred to as a “polishing workpiece”) and the method for making the same, and more particularly, to a sheet for mounting a workpiece to be polished and the method for making the same which are used in the chemical mechanical polishing process.
2. Description of the Related Art
Polishing generally refers to a wear control for a preliminary coarse surface in the process of chemical mechanical polishing (CMP), which makes the slurry containing fine particles evenly dispersed on the upper surface of a polishing pad, and at the same time places a polishing workpiece (i.e., a workpiece to be polished) against the polishing pad and then rubs the workpiece repeatedly with a regular motion. The polishing workpiece may be objects such as a semiconductor, a storage medium substrate, an integrated circuit, an LCD flat-panel glass, an optical glass and a photoelectric panel. During the polishing, a sheet must be used for carrying and mounting the polishing workpiece, and the quality of the sheet directly influences the polishing effect of the polishing workpiece.
Referring to FIG. 1, a schematic view of a polishing device with a conventional sheet disclosed in U.S. Pat. No. 5,871,393 is shown. The polishing device 1 includes a lower base plate 11, a sheet 12, a polishing workpiece 13, an upper base plate 14, a polishing pad 15 and slurry 16. The sheet 12 is adhered to the lower base plate 11 through an adhesive layer 17 and is used for carrying and mounting the polishing workpiece 13. The polishing pad 15 is mounted on the upper base plate 14.
The operation mode of the polishing device 1 is as follows. First, the polishing workpiece 13 is mounted on the sheet 12, and then both the upper and lower base plates 14 and 11 are rotated and the upper base plate 14 is simultaneously moved downwards, such that the polishing pad 15 contacts the surface of the polishing workpiece 13. A polishing operation for the polishing workpiece 13 may be performed by continuously supplementing the slurry 16 and using the polishing pad 15.
Referring to FIG. 2, a local schematic view of the sheet of FIG. 1 is shown. The sheet 12 is of a single-layer structure, the material of which is generally PU (polyurethane), a kind of foaming material. The sheet 12 is formed by a wet process, and thus a plurality of continuous foaming holes 121 exists in the interior of the sheet 12. The disadvantage of the sheet 12 is that the slurry 16 tends to be inhaled through the foaming holes 121 during the polishing process, which causes changes in the hardness and physical property of the sheet 12, such that the polishing condition needs to be readjusted. Furthermore, the lifetime of the sheet 12 is reduced. In addition, the sheet 12 is formed by the wet process which results in an excessively low planarity, and it is very difficult to achieve a generally uniform thickness above 0.5 mm. Finally, the foaming holes 121 within the sheet 12 cause the phenomenon of air wrapping when the sheet 12 adsorbs the polishing workpiece 13, thus resulting in a poor adhesion and a possible crack during the polishing process as well as an uneven polished surface after the polishing of the polishing workpiece 13.
Consequently, there is an existing need for a sheet for mounting a polishing workpiece and the method for making the same to solve the above-mentioned problems.